This invention relates to heat exchangers for physiologic fluids such as blood and blood-related fluids. Examples include stand alone heat exchangers used to maintain a patient""s blood at a predetermined temperature; the heat exchanger components of other devices, such as oxygenators used to maintain a patient""s blood at a predetermined temperature while replacing carbon dioxide in the blood with oxygen; heat exchangers used to cool cardioplegia solutions; and the like.
Heat exchangers of the well-known xe2x80x9cshell and tubexe2x80x9d type are widely used in the medical field for physiologic fluids, such as blood, blood-related fluids, blood-based and non-blood based cardioplegia solutions (including crystalloid solutions), cell culture media, cell suspensions, proteins, and microcapsule suspensions. (For convenience, the term xe2x80x9cbloodxe2x80x9d should be understood to include all such types of fluids unless specifically indicated otherwise.) Typically, the physiologic fluid is continuously or intermittently pumped through the heat exchanger and a suitable heat transfer fluid such as water is also pumped through the heat exchanger, physically separated from the physiologic fluid but capable of releasing or absorbing energy to or from the physiologic fluid. The water is either heated or cooled externally of the heat exchanger to maintain the physiologic fluid at a predetermined desired temperature.
One type of heat exchanger comprises tiny hollow fibers made of a polymeric material. Water entering the heat exchanger may flow around the outside surfaces of these fibers, while the physiologic fluid flows inside the fibers, or vice versa. The portion of the heat exchanger containing fluid which flows inside the fibers is known as the xe2x80x9ctubexe2x80x9d side, and the portion of the heat exchanger containing fluid which surrounds the fibers is known as the xe2x80x9cshellxe2x80x9d side.
The first general embodiment of the invention is a polymeric heat exchange material which has higher resistance to elecrical discharge through the material. The second general embodiment of the invention is a method and apparatus for maintaining electrical charge equilibrium between the xe2x80x9ctubexe2x80x9d side and the xe2x80x9cshellxe2x80x9d side of a polymeric heat exchanger, but the invention is not limited to only the tube-and-shell type of heat exchangers. The method comprises any technique for creating at least one electrical bridge between the tube side and the shell side. The apparatus comprises at least one electrical bridge between the tube side and the shell side. The only substantive requirement for the electrical bridge is that it permits sufficient current density to reduce the charge differential (or voltage potential) between the tube side and the shell side to a level below that at which electrical charge-induced breakdown of the polymeric material occurs. Since it is only necessary to equalize the charge between the tube and shell sides of the heat exchanger, an earth ground is not required. The two general embodiments may be employed separately or in combination.